Bobbin case for sewing machines

ABSTRACT

A bobbin case for a lockstitch sewing machine having a double screw to provide a tension which is adjustable within a predetermined range in order to obtain a proper bobbin thread tension for a desired stitch. The double screw comprises a sealed inner member which is factory adjusted to exert the highest tension of the range, and an outer member which is adjusted by a sewing machine operator to relieve the pressure applied by the inner screw member. A stop rivet engages the outer screw member at a particular position to establish the lowest tension of the range. The double screw acts upon a leaf spring which bears against the bobbin holddown arm to provide a tension resisting withdrawal of the thread wrapped on the bobbin. A double tension leaf spring is used to eliminate overstressing. A screw used to position the spring on the bobbin case has a ball-type head to permit a rocking motion which reduces the amount of deflecting or bending of the spring when the tension is applied.

United States Patent [72] Inventor Lionel J. Coulombe 3,154,035 10/1964 Edwards et a1. 1 12/184 l A I No Primary Examiner-Alfred R. Guest [22] g octz 1969 Attorneys-Marshall J. Breen, Chester A. Williams, Jr. and

45 1 Patented Mar. 9, 1971 [73] Assignee The Singer Company w w p New York ABSTRACT: A bobbin case for a lockstitch sewing machine having a double screw to provide a tension which is adjustable [54 1 BQBBIN CASE FOR SEWING MACHINES within a predetermined range in order to obtain a proper bob- 8 Chins 3 Drawing 13 bln thread tension for a desired stitch. The double screw comprises a sealed inner member which is factory adjusted to exert [52] US. Cl. 112/229 the highest tension of the range and an outer member whichv is [51] Dosh 57/14 adjusted by a sewing machine operator to relieve the pressure [50] Field ofselrcll 112/233, applied by the inner screw member A stop rivet engages h 229 outer screw member at a particular position to establish the lowest tension of the range. The double screw acts upon a leaf. [56] References cued spring which bears against the bobbin holddown arm to pro- UNITED STATES PATENTS vide a tension resisting withdrawal of the thread wrapped on p the bpbbrn. A Aiouble tenson Emits P1111515 used to ezlilmllraiage 1 er. overs ressrng. screw use to posl 1011 e spring on e 0 2,746,408 5/1956 Ayres 1 12/229 bin case has a balltype head to pennit a rocking motion which 2,763,227 9/1956 Howard 1 12/231 reduces the amount of deflecting or bending of the spring 3,1 15,855 12/ 1963 Ketterer 1 12/184 when the tension is applied.

PATENTEUMAR 9|97l 3.666.616

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Lionel J. Coulombe 515i; Wm 744W 43 W ATTORNEY CASE lFUllt SEWHNG MAQIES 7 BACKGROUND OF THE INVENTION There are many instances when an operator using a locltstitch sewing machine needs to adjust the tension of the bobbin thread, as well as the tension of the needle thread, to obtain a desired stitch, wherein a factory preset bobbin thread tension which cannot be adjusted by the operator would not be satisfactory in the formation of different types of stitches. For example, a balanced straight stitch would usually require a greater bobbin thread tension than a balanced zigzag stitch, wherein a bobbin thread tension which is factory adjusted for only one of these balanced stitches could not produce the other balanced stitch properly.

A bobbin case for lockstitch sewing machines having an ad justable tensioning device which acts upon a leaf spring bearing against a bobbin holddown arm to provide a tension on the bobbin thread for a desired stitch is well known, as shown in US. Pat. Nos. 3,115,855 and 3,154,035 to Ketterer and Edwards et al. respectively. The above tensioning device generally comprises a single screw in contact with the leaf spring, whereby the pressure of the screw against the leaf spring is adjusted by the operator to obtain a wide range of tensions on the bobbin thread. However, the high and low ends of the wide range usually are not employed to obtain the desired stitch, whereby the wide range makes it very time consuming for the operator to obtain the proper bobbin thread tension. Also, the leaf spring may be easily overstressed by the operator frequently turning the screw to exert the maximum pressure on the leaf spring, which results in the loss of the effectiveness of the leaf spring upon the bobbin holddown arm, whereby the operator will no longer be able to obtain the proper bobbin thread tension for the desired stitch.

SUMMARY OF THE iNVENTlON l his invention relates to sewing machines of the lockstitch type provided with a bobbin and bobbin case for holding thread and more particularly relates to bobbin thread tensioning means to obtain a desired stitch. The tensioning means comprises an operating element which is adjustable within a predetermined range to exert a desired pressure against an elastic element, whereby the elastic element bears upon a bobbin holddown arm so that a tension is provided on the bobbin thread to produce the desired stitch.

it is an object of this invention to provide a bobbin case for a lockstitch sewing machine having adjustable tension means for the bobbin thread.

it is further an object of this invention to provide a bobbin thread tensioning means which is quickly adjustable within a predetermined range to produce a desired stitch.

it is another object of this invention to provide a bobbin thread tensioning means of the above character which prevents the adjustable operating element from overstressing the elastic element.

BRlEF DESCRlPTIQN OF THE DRAWINGS Having in mind the above and other objects that will be evident from an understanding of this disclosure, the invention comprises the devices, combinations and arrangements of parts as illustrated in the presently preferred embodiment of the invention, which is hereinafter set forth in such detail as to enable those skilled in the art readily to understand the function, operation, construction and advantages of it, when read in conjunction with the accompanying drawings in which:

lFlG. ll represents a top plan view of a bobbin case embodying the invention;

FIG. 2 represents a bottom plan view of the bobbin case illustrated in FIG. l; and 1 HS. 3 represents an enlarged cross-sectional view of the bobbin case taken substantially along line 3-3 of FIG. ll.

A lockstitch sewing machine to which this invention has been applied is substantially that illustrated and described in detail in the US. Pat. of Edwards et al. No. 3,154,035, Get. 27, 1964, which includes stitch forming instrumentalities and a control mechanism for initiating bobbin thread replenishing, determining selectively the amount of thread to be replenished on the bobbin, and terminating the operation of the bobbin thread replenishing operation, wherein the above patent of Edwards et al. may be referred to for the particular details of the construction of the sewing machine.

Referring to FIGS. 1 and 2, a bobbin case l is shown which is a modification of the bobbin case disclosed in the above patent of Edwards et a1. whereby the bobbin case 1 may be used effectively in lieu of the bobbin case of the patent. The following general description of the bobbin case 1 will be sufficient to those skilled in the sewing art for an understanding of the detailed description of this invention contained hereinbelow.

The bobbin case i is journaled in the sewing machine looptalrer (not shown) and restrained against rotation, wherein an ordinarily free turning bobbin (not shown) is supported in the bobbin case 1. A top flange of the bobbin rests on the bobbin case 1 and is centered thereon by a spring biased bobbin holddown arm 2 pivoted on a pin 3 which is secured in the body of the bobbin case ll, shown in FIG. 3. The bobbin holddown arm 2 is formed with a depending spherical protuberance 4, shown in Fit]. 2, which is accommodated in a spherical seat formed in the top flange of the bobbin.

Disposed in a slot formed in the body of the bobbin case 1 and pivoted therein by a pin 5 is an arm 6 of a bobbin thread sensing member 7. The inturned free extremity of the arm 6 is formed with a vertically enlarged, slightly concave thread engaging shoe shown in FIG. 2, which projects inwardly from the body of the bobbin case 1 and is disposed between the flanges of the bobbin. Extending from the bottom edge of the thread engaging shoe 8, the thread sensing member 7 is formed with a cam surface 9 which is engageable with the rim of the bobbin winding member (not shown) to impart a frictional resistance when a predetermined quantity of thread is wound on the bobbin.

The construction of the bobbin case i thus far described is similar to that described in greater detail in the abovereferenced U.S. Pat. No. 3,l54,035 to which reference may be had.

The bobbin holddown arm 2, in bearing downwardly on the bobbin housed within the bobbin case 1, thus provides a frictional force between the bobbin and the bobbin case 1, thus provides a frictional force between the bobbin and the bobbin case 1 resisting turning of the bobbin and providing a tension on the bobbin thread during the sewing operation. This tension is adjustable within a predetermined range in order to obtain a proper bobbin thread tension for a desired stitch. A detailed description of this invention which produces the above adjustable tension is set forth below.

As shown in FIG. 3, a portion 10 of the bobbin holddown arm 2 extends downwardly into a recess ll formed in an underneath portion of the body of the bobbin case l. A long leaf spring 12 and a short leaf spring 13 are housed within recess ill with the longer spring 112 being positioned between the arm portion 10 and the shorter spring l3, so that the spring l2. rests on and is supported by the spring 13 with an end portion M of the spring 212 bearing against the arm portion ill. The leaf springs 12., iii are held in place within the recess it by a screw l5 having an enlarged ball-type head in.

An aperture 17 is formed in an upper body portion of the bobbin case l and communicates with the recess ill. The aperture i7 is partially tapered to have an upper opening larger than the head l6 and a lower opening smaller than the head lid, so that the enlarged head lb engages the tapered sidewalls of the aperture 17, thereby preventing the head to from passing therethrough. The threaded body of the screw which has a cross section smaller than the lower opening of the aperture 17, extends through the aperture 17 into the recess 11. Within the recess 11, the screw 15 passes through an aperture 18 formed in the spring 12 and is screwed into a threaded aperture 19 formed in the spring 13 to secure the springs 12, 13 within the body of the bobbin case 1. The head 16 of the screw 15 normally will be positioned below the upper surface of the bobbin case 1 within the aperture 17 as shown in FIG. 3. A conventional screwdriver slot is formed in the head 16 to permit the screw 15 to be turned by a screwdriver.

A double screw 20 defines an adjustable tensioning device having an operating element which is adjustable within a predetermined range to exert a desired pressure against an elastic element formed by the leaf springs 12, 13. The double screw 21) comprises an outer member 21 and an inner member 24, where the member 24 is longer than the member 21. The outer screw member 21 is cylindrical and has an enlarged flat head 22 with a conventional screwdriver slot to permit the operator to turn the member 21 with a screwdriver. A portion 23 of the member 21 has external threads. A threaded aperture is formed longitudinally through the center of the member 21 to receive the inner screw member 24. The inner member 24, which is cylindrical, has an externally threaded portion 25 and a reduced end portion 26 extending longitudinally from the portion 25. A slot or the like is formed in the portion 25 to permit the member 24 to be turned in the factory with a proper tool to a predetermined position.

A stepped aperture 27 having a large upper opening and a small lower opening is formed in the upper body portion of the bobbin case 1 and communicates with the recess 11, where the aperture 27 is spaced from the aperture 17. The upper opening of the aperture 27 is large enough to receive the head 22 of the screw member 21, with the lower opening of the aperture 27 being threaded to receive the externally threaded portion 23 of the screw member 21. The aperture 27 is located above the end portions of the leaf springs 12, 13 which are opposite to the end portion 14 of the spring 12.

The screw member 21 is threaded downwardly into the aperture 27 until the head 22 abuts the step of the aperture 27. Now, the screw member 24 is threaded downwardly into the threaded aperture of the screw member 21 with the end portion 26 extending into the recess 11. Within the recess 11, the end portion 26 of the member 24 passes through an aperture 25 formed in the spring 12 and bears against an end portion 29 of the spring 13, where the aperture 28 is formed in an end portion of the spring 12 which is opposite to the spring end portion 14.

With the members 21, 24 positioned as above, a factory adjustment is made by turning the inner screw member 24 to move relative to the outer screw member 21 while exerting downward pressure on the leaf spring 13. The ball-type head 16 permits the screw 15 and the spring 13 to pivot slightly when the pressure of the screw member 24 on the spring end portion 29 is increased, thereby causing the opposite end portion 30 of the spring 13 to move upwardly. Therefore, the portion of the spring 12 which rests on the end portion 30 also is moved upwardly, thereby causing the end portion 14 of the spring 12 to exert upward pressure on the arm portion 10 of the bobbin holddown arm 2. The upward pressure on the arm portion 10 causes the arm 2 to pivot on the pin 3, thereby causing the opposite end portion of the arm 2 to exert downward pressure on the bobbin. The downward pressure on the bobbin resists the turning of the bobbin, thus providing a tension on the bobbin thread during the sewing operation.

The inner screw member 24 is turned during the factory adjustment until a desired maximum bobbin thread tension is obtained. The maximum tension is usually to grams. After the above factory adjustment is made, the opening of the threaded aperture of the screw member 21, which is above the inner member portion 25, may be filled with a conventional sealing material to seal the inner member 24 within the outer member 21 so that the operator cannot tamper with the factory adjustment for the maximum bobbin thread tension.

With the maximum bobbin thread tension of the range having been set at the factory, the outer screw member 21 may be adjusted by the operator to obtain a lower bobbin thread tension. In order to relieve the pressure applied by the inner screw member 24 which controls the bobbin thread tension, the outer screw member 21 is screwed out of the threaded opening of the aperture 27 to obtain lower tensions, with the head 22 of the member 24 moving upwardly away from the step of the aperture 27. The inner screw member 24 turns together with the outer screw member 21 when the latter is turned by the operator because the frictional force between the members 21 and 24 when threaded together is greater than the frictional force between the member 24 and the spring 13 when the member end portion 26 bears against the spring end portion 29, this being true whether the outer screw member 21 is being screwed into or out of the threaded opening of the aperture 27. The operator turns the outer screw member 21 either inwardly for higher tensions or outwardly for lower tensions until the desired bobbin thread tension is obtained.

After the double screw 20 is positioned in the aperture 27, a rivet 31 is secured in the body of the bobbin case 1 adjacent to the aperture 27. A head 32 of the rivet 31 is enlarged and extends over a portion of the upper opening of the aperture 27 so that the head 22 of the screw member 21 abuts the head 32 of the rivet 31 when the screw member 21 is screwed outwardly a predetermined amount. The rivet 31 acts as a stop to prevent any further upward movement or the removal of the double screw 20 and thereby establishes the lowest tension of the range, usually 20 to 25 grams. Thus, the double screw 20 is restricted to movement between the stop rivet 31 for the lowest tension and the step of the aperture 27 for the highest tension. Obviously, the stop rivet 31 and the step of the aperture 27 are spaced apart a distance greater than the longitudinal length of the head 22 of the screw member 21.

Though the above bobbin case 1 may be constructed with only one leaf spring, the two leaf springs 12, 13 are desired to provide a double tension spring for consistent tension settings and to eliminate overstressing which results in the loss of the required tension.

The ball-type head 16 of the screw 15 permits the screw 15 and the leaf spring 13 to rock slightly when the tension is varied by means of the operator adjusting screw 21. This rocking motion of the spring 13 and the screw 15 reduces the usual amount of deflecting or bending of a spring when tension is applied, particularly when applying the higher tensions.

Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to a preferred embodiment of my invention which is for purposes of illustration only and not to be construed as a limitation of the invention.

lclaim:

1. A bobbin case comprising a body, a spring biased arm being pivotally mounted on said body for exerting pressure on a bobbin housed within said bobbin case to obtain a bobbin thread tension, and an adjustable tensioning device cooperating with said arm to provide a range of bobbin thread tensions, said device having first means connected to said body and second means connected to said first means, said second means moving relative to said first means and said body to set the highest tension of said range, said first and second means moving together relative to said body to obtain a lower tension of said range for a desired stitch.

2. A bobbin case according to claim 1 wherein abutment means are positioned adjacent to said first means to restrict the movement of said first means between a first position for the highest tension and a second position for the lowest tension of said range.

3. A bobbin case according to claim 1 wherein said first means comprises a screw, said screw being screwed into a threaded aperture formed in said body.

d. A bobbin case according to claim 3 wherein said second means comprises a screw, said second means screw being screwed into a threaded aperture formed longitudinally in said first means screw, whereby said second means screw moves together with said first means screw when said first means screw is turned in said body.

5. A bobbin case according to claim 3 wherein said threaded aperture is stepped to form a first abutment, a rivet being positioned adjacent to said threaded aperture, said rivet having an enlarged head extending over a portion of said threaded aperture to form a second abutment, said screw having an enlarged head engageable with said first and second abutments, said abutments being spaced apart a distance greater than the longitudinal length of said screwhead, said screwhead being restricted to movement between said abutments.

05. A bobbin case according to claim 5 wherein said second means comprises a screw, said second means screw being screwed into a threaded aperture formed longitudinally in said first means screw, whereby said second means screw moves together with said first means screw when said first means screw is turned in said body for movement between said first and second abutments.

7. A bobbin case according to claim 1 wherein said adjustable tensioning device is in bearing contact with spring means and said spring means is in bearing contact with said arm, said spring means providing consistent tension settings and eliminating overstressing, said spring means comprising a first leaf spring supporting a second leaf spring, and means connecting said first leaf spring to said body.

8. A bobbin case according to claim 7 wherein said means connecting said first leaf spring to said body comprises a screw having a ball-type head, said ball-type head being held within an aperture formed in said body, said screw extending through an aperture formed in said second leaf spring and being screwed into a threaded aperture formed in said first leaf spring, so that said ball-type head permits said screw and said first leaf spring to rock slightly when the tension is varied by said adjustable tensioning device, whereby said rocking reduces the amount of deflecting of said spring means. 

1. A bobbin case comprising a body, a spring biased arm being pivotally mounted on said body for exerting pressure on a bobbin housed within said bobbin case to obtain a bobbin thread tension, and an adjustable tensioning device cooperating with said arm to provide a range of bobbin thread tensions, said device having first means connected to said body and second means connected to said first means, said second means moving relative to said first means and said body to set the highest tension of said range, said first and second means moving together relative to said body to obtain a lower tension of said range for a desired stitch.
 2. A bobbin case according to claim 1 wherein abutment means are positioned adjacent to said first means to restrict the movement of said first means between a first position for the highest tension and a second position for the lowest tension of said range.
 3. A bobbin case according to claim 1 wherein said first means comprises a screw, said screw being screwed into a threaded aperture formed in said body.
 4. A bobbin case according to claim 3 wherein said second means comprises a screw, said second means screw being screwed into a threaded aperture formed longitudinally in said first means screw, whereby said second means screw moves together with said first means screw when said first means screw is turned in said body.
 5. A bobbin case according to claim 3 wherein said threaded aperture is stepped to form a first abutment, a rivet being positioned adjacent to said threaded aperture, said rivet having an enlarged head extending over a portion of said threaded aperture to form a second abutment, said screw having an enlarged head engageable with said first and second abutments, said abutments being spaced apart a distance greater than the longitudinal length of said screwhead, said screwhead being restricted to movement between said abutments.
 6. A bobbin case according to claim 5 wherein said second means comprises a screw, said second means screw being screwed into a threaded aperture formed longitudinally in said first means screw, whereby said second means screw moves together with said first means screw when said first means screw is turned in said body for movement between said first and second abutments.
 7. A bobbin case according to claim 1 wherein said adjustable tensioning device is in bearing contact with spring means and said spring means is in bearing contact with said arm, said spring means providing consistent tension settings and eliminating overstressing, said spring means comprising a first leaf spring supporting a second leaf spring, and means connecting said first leaf spring to said body.
 8. A bobbin case according to claim 7 wherein said means connecting said first leaf spring to said body comprises a screw having a ball-type head, said ball-type head being held within an aperture formed in said body, said screw extending through an aperture formed in said second leaf spring and being screwed into a threaded aperture formed in said first leaf spring, so that said ball-type head permits said screw and said first leaf spring to rock slightly when the tension is varied by said adjustable tensioning device, whereby said rocking rEduces the amount of deflecting of said spring means. 